<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
  <script>
      var a = 15;
      var b = "Hello World";
      var c = true;
      var d;
      console.log("typeof(a) : "+ typeof a);
      console.log("typeof(b) : "+ typeof b);
      console.log("typeof(c) : "+ typeof c);
      console.log("typeof(d) : "+ typeof d);
  </script>
</body>
</html>